The present application relates to vehicle air braking systems, and is particularly directed to a slack adjuster for a drum brake of a vehicle air braking system, such as a heavy vehicle air braking system.
A typical drum brake includes a brake shoe that engages a wheel drum to transmit braking torque through a brake spider to a wheel axle. One end of the brake shoe is pivotable against an anchor pin that is attached to one side of the brake spider. A cam follower roller is disposed at the other end of the brake shoe. When a service brake application occurs, a camshaft located on the side of the brake spider opposite the anchor pin is actuated to rotate about its longitudinal central axis. As the camshaft rotates about its longitudinal central axis, a cam surface of an S-cam mounted on the camshaft acts against the cam follower roller to pivot the brake shoe about the anchor pin. As the brake shoe pivots about the anchor pin, the brake lining of the brake shoe frictionally engages the wheel drum to transmit braking torque through the brake spider to the wheel axle and thereby to decelerate and brake the vehicle.
In a typical S-cam type of drum brake, a pneumatic system is linked by an air line to a spring brake chamber. The spring brake chamber is connected by a push rod and clevis to an arm of a slack adjuster. The slack adjuster is the link between the spring brake chamber and the camshaft. More specifically, the slack adjuster includes a yoke to which the push rod from the spring brake chamber is fastened, and a spline that is installed on a spline of the camshaft. The slack adjuster converts a linear force of the push rod from the spring brake chamber into a torsional force that acts on the camshaft to rotate the camshaft about its longitudinal central axis. The entire slack adjuster operates as a unit, rotating as a lever with the camshaft as the brakes are applied or released.
The slack adjuster is also equipped with an adjusting mechanism to provide a means of adjusting for brake lining wear. In particular, the clearance between the brake lining and the wheel drum is adjusted to compensate for the gradual wear on the brake lining of the brake shoe. The adjusting mechanism is usually a clutch-type mechanism that continuously adjusts in very small increments as wear of the brake lining and the wheel drum occurs. Accordingly, those skilled in the art continue with research and development efforts in adjusting mechanisms of slack adjusters for S-cam drum brakes.